1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel capable of preventing the use of heavy metal harmful to the human body in forming a black matrix and minimizing an area of a dummy region except an effective image display part.
2. Discussion of the Related Art
In general, a liquid crystal display apparatus is a display device in which data signals including image information are individually supplied to unit pixels arranged in a matrix form, and the light transmittance of the unit pixels is controlled to display a desired image.
Thus, the liquid crystal display device includes a liquid crystal display panel where the unit pixels are arranged in a matrix form, and a driver integrated circuit (IC) for driving the unit pixels.
In the liquid crystal display panel, a thin film transistor array substrate and a color filter substrate are attached to each other so as to face into each other and have a certain interval (generally, referred to as a cell-gap) therebetween, and, at the cell-gap, a liquid crystal layer is formed.
The thin film transistor array substrate and the color filter substrate are attached to each other by a seal pattern formed along the outer edge of an effective image display part. At this time, a spacer is formed on the thin film transistor array substrate or the color filter substrate, thereby-forming a certain cell-gap therebetween.
At outer surfaces of the substrates, a polarizing plate, a retardation plate and the like are installed. Such a plurality of components are constructed to vary the state of light and a refraction ratio of light passing through in order to have a liquid crystal display device having a high brightness and a contrast characteristic.
At the liquid crystal display panel where the thin film transistor array substrate and the color filter substrate face into and are attached to each other, a common electrode and a pixel electrode are formed to apply an electric field to the liquid crystal layer. That is, a voltage applied to the pixel electrode is controlled while a voltage is applied to the common electrode, thereby individually controlling light transmittance of the unit pixels. In order to control the voltage applied to the pixel electrode for each unit pixel separately, a thin film transistor used as a switching device is formed at each unit pixel.
Liquid crystal display devices are generally classified into twisted nematic (TN) mode liquid crystal display panels and in-plane switching (IPS) mode liquid crystal display panels.
In the TN mode liquid crystal display panel, a pixel electrode is formed on a thin film transistor array substrate at each unit pixel, and a common electrode is formed at an entire surface of a color filter substrate. Thus, a liquid crystal layer is driven by an electric field between the pixel electrode formed on the thin film transistor array substrate and the common electrode formed on the color filter substrate.
In the IPS mode liquid crystal display panel, a pixel electrode and a common electrode are formed on a thin film transistor array substrate at a predetermined interval then. Thus, a liquid crystal layer is driven by a horizontal electric field between the pixel electrode and the common electrode formed on the thin film transistor array substrate.
FIG. 1 is an exemplary view illustrating a plane structure of a liquid crystal display panel where the thin film transistor array substrate and the color filter substrate face into and are attached to each other.
In FIG. 1, the thin film transistor array substrate 101 faces into and is attached to the color filter substrate 102, and an edge of one long side thereof and an edge of one short side thereof are protruded compared to the color filter substrate 102.
At a region where the substrates 101 and 102 are attached to each other, an image display part 113 is provided, where unit pixels are formed in a matrix form to display an image. A seal pattern 116 is formed along the outer edge of the image display part 113.
A gate pad part 114 connected with gate lines of the image display part 113 is provided. At an edge region of one short side of the thin film transistor array substrate 101 that extends beyond the color filter substrate 102.
A data pad part 115 connected with data lines of the image display part 113 is provided. At an edge region of one long side of the thin film transistor array substrate 101 extends beyond the color filter substrate 102.
The gate pad part 114 supplies a scan signal supplied from a gate driver integrated circuit to the gate lines of the image display part 113, and the data pad part 115 supplies image information supplied from a data driver integrated circuit to the data lines of the image display part 113.
On the thin film transistor array substrate 101, the gate lines to which the scan signal is applied, and the data lines to which the image information is applied, intersect one another, so that the unit pixels are defined in a matrix form. At the intersection, a thin film transistor is provided for switching the unit pixel.
On the color filter substrate 102, a red, green or blue color filter corresponding to a unit pixel is provided, and a black matrix is provided to prevent a leakage of light generated from a back-light and to prevent a mixture of colors from adjacent unit pixels.
In case of the TN mode liquid crystal display panel, a pixel electrode is provided at the thin film transistor array substrate 101 and a common electrode is provided at the color filter substrate 102 to drive a liquid crystal layer. In case of the IPS mode liquid crystal display panel, a pixel electrode and a common electrode are provided at the thin film transistor array substrate 101 to drive a liquid crystal layer.
The thin film transistor array substrate 101 and the color filter substrate 102 are have a cell-gap therebetween maintained by a spacer so as to separate one from the other by a fixed distance. They are attached to each other by a seal pattern 116 formed at the outer edge of the image display part 113, and thus constitute a liquid crystal display panel 100. At one side of the seal pattern 116, a liquid crystal injection hole is provided for injecting liquid crystal between the thin film transistor array substrate 101 and the color filter substrate 102 that are attached to each other. The liquid crystal injection hole is sealed after an injection of the liquid crystal is terminated.
FIG. 2 illustrates an embodiment of a sectional structure of a color filter substrate for a region ‘A’ of FIG. 1 in case of the TN mode liquid crystal display panel.
With reference to FIG. 2, the color filter substrate includes a black matrix 202 made of a chrome material, formed at a predetermined region extended from one end portion of a transparent substrate 201 and at a boundary region of pixels, preventing a leakage of light generated from a back-light, and preventing a color mixture of the adjacent pixels; a red, green or blue color filter 203 partially overlapping with the black matrix 202, and formed to correspond to a unit pixel; a common electrode 204 formed on the entire surface of upper parts of the black matrix 202 and the color filter 203; and a seal pattern 205 formed on a structure that the black matrix 202 and a common electrode 204 are laminated.
In order to form the black matrix 202 on a color filter substrate of the TN mode liquid crystal display panel, a thin film made of a chrome material is deposited in a film process, such as sputtering, and the deposited thin film is patterned through a photolithography process.
The seal pattern 205 is formed on a structure such that the black matrix 202 made of the chrome material and the common electrode 204 made of a transparent metal material are laminated.
As above, for the black matrix 202 formed on the color filter substrate of the related art of TN mode liquid crystal display panel, a thin film made of a chrome material, a heavy metal to the human body, toxic is used.
FIG. 3 illustrates an embodiment of a sectional structure of a color filter substrate for a region ‘A’ of FIG. 1 in the case of the IPS mode liquid crystal display panel.
With reference to FIG. 3, the color filter substrate includes a black matrix 302 made of a resin material, formed at a region constantly separated from one end portion of a transparent substrate 301 and at a boundary region of pixels, preventing a leakage of light generated from- a back-light, and preventing a color mixture of adjacent pixels; a red, green, or blue color filter 303 partially overlapping with the black matrix 302, and formed to correspond to a unit pixel; an over-coat layer 304 formed at an entire surface of an upper part of a transparent substrate 301 including the black matrix 302 and the color filter 303; and a seal pattern 305, formed at an upper surface of the over-coat layer 304 formed on the edge portion of the transparent substrate 301.
Unlike the TN mode liquid crystal display panel, the black matrix 302 formed at the color filter substrate of the IPS mode liquid crystal display panel is formed of an organic film such as a resin material.
In the IPS mode liquid crystal display panel, a liquid crystal layer is driven by an electric field between a pixel electrode and a common electrode formed on a thin film transistor array substrate. Therefore, in case that the black matrix 302 formed on the color filter substrate is formed of a thin film made of a metal material such as chrome, an electric field between the pixel electrode and the common electrode is distorted thereby causing deficiency in driving the liquid crystal layer. Accordingly, the black matrix 302 formed on the color filter substrate of the IPS mode liquid crystal display panel is formed of a thick film which is made of an organic film such as a resin material.
The over-coat layer 304 is formed at an entire surface of an upper part of the transparent substrate 301 including the black matrix 302 and the color filter 303 in order to planarize the surface.
However, because the seal pattern 305 formed at the color filter substrate of the IPS mode liquid crystal display panel is formed at an upper surface of the over-coat layer 304 that is formed on the edge portion of the transparent substrate 301, a region where the seal pattern 305 is formed and separate a region where the black matrix 302 is formed are required. Thus, a dummy area is increased relative to an effective image display part, and consequently, the size of the IPS mode liquid crystal display panel must be increased. In addition, since the black matrix 302 is not formed at an edge portion of the transparent substrate 301 at which the seal pattern is formed 305 due to a problem in adhering the black matrix 302 and the seal pattern 305, light generated from a back light leaks at the edge portion of the transparent substrate 301, thereby degrading the image quality of the liquid crystal display panel.
In addition, a black matrix made of a chrome material is formed through a thin film process in the TN mode liquid crystal display panel, but a black matrix made of an organic material is formed through a thick film process in the IPS mode liquid crystal display panel. Therefore, separate individual processes for producing the color filter are performed according to the TN mode and the IPS mode, increasing the complexity of and degrading the efficiency on the use of clean rooms.